Deposition of minerals in hair is an unavoidable phenomenon. Well water, used by many communities around the country and around the world, is enriched with a wide array of minerals. Copper and iron ions can also leach from pipes into water, especially where water supplies are chlorinated periodically. Swimmers encounter a constant source of copper in the form of certain algicides added frequently to swimming pools. Many of the swimmers develop a greenish tint as copper accumulates in their hair. This greenish tint is independent of hair type or color. Dark and brown hair adsorb as much copper as light blonde hair although the greenish color obviously is not readily visible.
Many cosmetic hair products contain, by design, certain amounts of minerals, such as magnesium, iron or copper to perform specific functions. Products which fall into this category include hair conditioners containing magnesium sulfate and hair colorants containing lead acetate, henna, other plant extracts, or metallic pretreatments.
Hair is a strong adsorbent of these metals. Binding is so strong that once these multivalent cations are captured by the anionic sites on the fiber, they are hard to elute off these sites. As a result, there is a gradual metallic build-up which only intensifies with time. The extent to which minerals in general bind to hair depends on several factors such as condition and porosity, length of the fiber, and levels as well as duration of exposure.
This metal build-up can lead to a range of undesirable, and sometimes adverse, effects. Metals like copper, lead and iron, can interfere with chemical treatments such as hair coloring and permanent waving. Iron- and/or copper-contaminated hair may experience uneven and unpredicted color deposit because of variations in hair porosity and mineral build-up. Such variations in mineral build-up lead to differences in the rate of catalysis and formation of dye molecules along the length of the hair shaft, causing the uneven color deposit. Iron can also interfere with permanent waving, by reacting with reducing agents such as thioglycolic acid and its derivatives, to produce an undesirable purple color. Both iron and copper can catalyze the decomposition of the peroxide in the neutralizing solution of the rebonding step, hence reducing its capacity to fully reoxidize the thiol groups. This can lead to a weakened perm and a fragile hair.
Metal build-up can also result in serious breakaway exothermic reactions which may precipitate severe injury to the scalp and facial areas. An example of such a nightmare experienced by the majority of salon operators, is during bleaching or highlighting of hair significantly contaminated with heavy metals. The temperature under these circumstances may rise to the boiling point in as little as five minutes.
Normal levels of minerals in uncontaminated hair have been measured by several investigators and the following concentration ranges have been reported: copper, 17-38 parts per million (ppm); calcium, 140-2450 ppm; magnesium, 20-450 ppm; iron, 6-300 ppm; and lead, 5-7 ppm (Weber et. al., J. Tropical Pediatrics (1990) 36:230-34). When build-up levels significantly exceed the normal ranges, due to exogenous accumulation, discoloration of the hair becomes visible. Iron casts a typical rusty look to the hair, lead gives it a black tone, copper deposits a greenish tint, while calcium and magnesium deposits are colorless. In the reported cases of green hair, the depth of the greenish tint is proportional to the amount of copper adsorbed onto the hair. A hint of green can be noticed on light blonde hair at copper levels as low as 300 ppm. Copper content of hair from people with green hair fluctuates through a wide range, and values of 1500 to 17500 ppm have been reported by different investigators (Roomans and Forslind, Ultrastruc. Pathol., (1980) 1:301-7). A value of about 5000 ppm has been documented quite frequently. In the laboratory, levels as high as 34,000 ppm have been recorded when extensively bleached hair was used (Edman and Marti, J. Soc. Cosmet. Chem. (1961) 12:133-45).
The problem of mineral adsorption by the hair has been seriously addressed during the last three decades, and many efforts have been directed towards finding a remedy, but none has been very successful. As far back as half a century ago, hair dressers recommended hot oil treatment for removing the green tint from hair. In addition to being messy, the remedy is for the most part, ineffective. Hilderbrand and White (Clin. Chem. (1974) 20:148-51) tried several washing procedures which included the chelating agent ethylenediaminetetra-acetic acid disodium salt (EDTA-Na.sub.2). Their conclusion was that no significant effect was observed with removal of copper, and only partial success was attained with removal of calcium, magnesium and zinc. Similarly, Holmes and Goldsmith (New Engl. J. Med. (1974) 291:1037) were not able to remove the green tint from hair with either water, acetone, ethanol, or hexane extraction. Following a parallel path, Nordlund et. al. (Arch. Dermatol. (1977) 113:1700) found that elements adsorbed to the hair resist elution by washing, boiling, organic solvents and EDTA. They concluded that standard wash procedures do not remove exogenously adsorbed metals. Using a more drastic procedure, Assarian and Oberleas (Clin. Chem. (1977) 23:1771-2) found that only 45% of copper could be removed by a wash system containing a combination of harsh organic solvents such as acetone and ether, and detergents. Under conditions of high contamination of zinc and copper, McKenzie (Am. J. Clin. Nutr. (1978) 31:470-80) reported that a cleansing solution containing EDTA-Na.sub.2 and a detergent could not elute all the copper.
In the late seventies, Ramachandra et. al. (J. Soc. Cosmet. Chem. (1979) 30:1-8), after experimenting with several cleansing treatments, showed that the adsorbed copper and the resultant green color cannot be washed off by normal shampooing or treatment with a detergent. In studies employing radioisotopes, Buckley et. al. (Am. J. Clin. Nutr. (1984) 40:840-46) noted that in all cases studied, no evidence was found that any washing procedure effectively removed all exogenous metal. More recently, Wilhelm et. al. (J. Anal. Toxicol. (1989) 13:17-21) tested the efficacy of EDTA and detergent solutions in removing adsorbed metals. Their conclusion also was that the removal of adsorbed elements after treatment with various metal-enriched aqueous solutions is not very effective.
The patent literature reveals very few references to the problem of metal contaminants in hair or other keratin fibers. U.S. Pat. No. 4,581,229, teaches of a composition based on lanthanum salts for removing heavy metals from hair. The reference is deficient for two reasons: (1) in the case of iron contaminated-hair, the level of contamination in the tested samples was too low (about 160 ppm) to give any statistical significance; and (2) in the case of copper, no quantitative data is presented other than the qualitative statement indicating a reduction of the greenish color. The patent, however, warns against the use of chelating and complexing agents in conjunction with lanthanum salts because of undesirable effects. On the other hand, U.S. Pat. No. 4,690,818 teaches of a cleansing formulation intended for conditioning and moisturizing of hair and/or skin. The formulation utilizes low levels (0.001-0.5%) of EDTA salts to remove metals from water and soften it during washing of hair or skin. In this instance, EDTA is used to sequester metal ions from the washing water and not the hair, and no claims of metal removal from hair are made. As will be shown below (Table 4), EDTA levels twenty times as high as the upper limit of what is specified in this patent, are ineffective for total removal of hair metal contaminants.
More recently, International Patent Application, No. WO 93/11737, filed Jun. 24, 1993 disclosed a composition for the removal of minerals, which includes the combination of acidifying agent, reducing agent, chelating agent, and gelling agent. The reasoning behind this composition is that, since chelation with EDTA had only marginal efficiency, the inclusion of an acidifying agent and a reducing agent was required to weaken the bonds between the minerals and the hair proteins.
In spite of the documented scientific and patent literature attesting to the absence of an effective hair cleansing treatment for metal contaminants, there are numerous commercial products on the market which claim the ability to demineralize contaminated hair. These claims are usually made, based on the mere inclusion in these products of a chelating agent. As pointed out in the literature review earlier, and as will be shown below, there is very little validity for these claims.
A metal-cleansing treatment for hair, wool, and other keratin material, therefore, is desperately needed. This cleansing treatment should be safe, effective against a wide range of divalent and trivalent metals, and mild enough to lift only metal and soil contaminants from the hair without modifying its color or affecting the integrity and structure of the fiber.